AU633665B2 - Mixed sintered metal materials based on borides, nitrides and iron binder metals - Google Patents

Abstract

The invention relates to mixed sintered metal materials based on high-melting borides and nitrides and low-melting iron binder metals having the composition: (1) 40-97% by volume of borides, such as titanium diboride and zirconium diboride; (2) 1-48% by volume of nitrides, such as titanium nitride and zirconium nitride; (3) 0-10% by volume of oxides, such as titanium oxide and zirconium oxide, with the proviso that components (2) and (3) may also be present as oxynitrides such as titanium and zirconium oxynitride; and (4) 2-59% by volume of low-carbon binder metals, such as iron and iron alloys and to processes for preparing the same.

Description

r- 63366o5 Form COMMONWEALTH OF AUSTRALIA PATENTS ACT 1952.69 COMPLETE SPECIFICATION

(ORIGINAL)

Class Int. Class Application Number: Lodged: Complete Specification Lodged: Accepted: Published: Priority SRelated Art: Name of Applicant Address of Applicant 0 Actual Inventor Address for Sevice a ELEKTROSCHMELZWERK KEMPTEN GMBH Herzog-Wilhelm-Strasse 16, 8000 Munchen 2, Germany DIETRICH LANGE, LORENZ SIGL and KARL-ALEXANDER SCHWETZ WATERMARK PATENT TRADEMARK ATTORNEYS.

LOCKED BAG NO. 5, HAWTHORN, VICTORIA 3122, AUSTRALIA Complete Specification for the invention entitled: MIXED SINTERED METAL MATERIALS BASED ON BORIDES, NITRIDES AND IRON BINDER

METALS

The following statement is a full description of this invention, including the best method of performing it known to Mixed sintered metal materials based on borides, nitrides and iron binder metals Sintered metals, which are understood as sintered materials consisting of metallic sintered materials based on high-melting carbides of the metals from Groups 4b to 6b of the Periodic Table and low-melting binder metals from the iron group, in particular cobalt, have been known for a long time. They are mainly used for the 00 machining technology and for controlling wear. For producing these sintered metals from the usually pulverulent o xsintering materials, the metal binders are necessary .o which must wet the sintering material during the sintering process with alloy formation (solution). It is only in this way that the tough/hard microstructure of the sintered metals, of which the WC-Co and TiC-WC-Co systems are best known, suitable for use is formed. It is also o°o iknown that binders from the iron group are also suitable for other high-melting metallic sintered materials such as borides and nitrides (compare "Ullmanns Enzyklopadie der techn. Chemie [Ullmann's Encyclopedia of Industrial Chemistry]", volume 12, 4th edition 1976, chapter "Sintered Metals", pages 515-521).

The systems TiB 2 -Fe, Co or Ni and ZrB 2 and Fe, Co o. r Ni have already been investigated in the 60s. It was then found that such alloys based on TiB 2 with up to Fe as binder are considerably harder than those based on WC-Co and TiC-WC-Co. Alloys based on ZrB 2 with Co and Ni are brittle and not resistant to oxidation, whereas Fe reacts with ZrB 2 to form tetragonal Fe 2 B and can thus not be used as a binder (compare papers by V.F. Funke et al.

and M.E. Tyrrell et al., abstracted in the book "Boron and Refractory Borides", edited by V.J. Matkovich, Springer-Verlag, Berlin-Heidelberg-New York, 1977, in chapter XIV, page 484, in conjunction with'Table 7 and 2 page 488 in conjunction with Table 8).

It was concluded from these results that evidently the suitable binder, which might compensate the disadvantages of the excessive brittleness and thus allow industrial use of such alloys in the field of cutting materials and other applications with high demands on the corrosion resistance, heat resistance and/or oxidation resistance, for these borides had not yet been found (compare loc. cit., page 489).

Alloys based on nitrides and carbonitrides of titanium and zirconium with a very high proportion of the binder, in particular iron, (at least 50% and higher) are particularly tough, but no longer very hard (HV 1050 1175) (compare US-A-4,145,213 of Oskarsson et al.).

*0.o Presumably, such materials are indeed less brittle than o the abovementioned boride-based systems. Because of their O low hardness, however, they are unsuitable for machining hard and high temperature-resistant materials, such as SiC-reinforced aluminium alloys.

Combinations based on diborides, in particular of titanium and zirconium, with carbides and/or nitrides, in *000 particular titanium nitride and titanium carbide, and *o with boride-based binders, such as in particular Co boride, Ni boride or Fe boride, do not lead to a solution o 0 o of the problem, since, although such materials are very hard and strong because of the boride binder, which is to be understood in particular as CoB, they are particularly brittle instead (compare US-A-4,379,852 of Watanabe et al.).

Finally, attempts have also already been made to add graphite, -hich is intended to react with oxygen present during the sintering step, to the known system based on titanium boride and, if appropriate,: titanium carbide with binders of iron, cobalt and nickel or alloys thereof before the mixture is sintered. In this way, it is said that cutting materials can be obtained which are both sufficiently hard and tough, so that they can be used in particular for the machining of aluminium and aluminium alloys (compare EP-B-148,821 of Moskowitz et 3 al., which is based on PCT application WO 84/04,713). By the reaction of graphite with titanium boride in the presence of iron, however, the formation of the undesired FezB phase is promoted, which is not only less hard than titanium diboride but also reduces the proportion of the ductile iron binder phase, so that the materials resulting from this are not only less hard, but also less tough.

It is therefore the object to provide mixed sintered metal materials based on high-melting borides and nitrides of metals from Group 4b of the Periodic Table and low-melting binder metals consisting of iron or iron alloys, which are highly dense, very hard, tough and o strong so that they can be used in particular as cutting a materials for hard and high temperature-resistant materials.

o .The mixed materials according to the invention o consist of 40%to 97% by volume of borides selected from the group comprising titanium diboride, zirconium diboride and solid solutions thereof, 1 to 48% by volume of nitrides selected from the group comprising titanium nitride and zirconium nitride, 0 to 10% by volume of oxides selected from the group comprisingtitanium dioxide and zirconium dioxide and 2 to 59% by volume of low-carbon iron and iron alloys and have the following properties: density at least 97% theoretical density, relative to the theoretically possible density of the total mixed material, grain size of the sintered material phase at most 5.5 im, hardness (HV 30) at least 1,200, bending fracture strength (measured by the 4-point method at room temperature) at least 1,000 MPa and 2\ o S' eS 1/2 S fracture a KI at least MPa m' ft Mixed, sintered metal materials, in which the I -C CLE~aZ=tt?~i~.. Il" ^.r 4 sintered material components consist of titanium boride and titanium nitride, which together make up 50 97% by volume, preferably 50 90% by volume and especially about 80% by volume, of the total mixed material have proved particularly suitable. Preferably, 2.5 -40% by volume of the sintered material components consist of titanium nitride. The remainder to make 100% by volume in the total mixed material is distributed over the oxides which may be present, if appropriate, preferably titanium dioxide, in a proportion of between 0 and 10% by volume, and the metallic binder phase consisting of the low-carbon iron or iron alloy. The alloy elements for low-carbon iron grades are preferably chromium or chromium/nickel mixtures.

0o o The mixed sintered metal materials according to the invention can be produced by processes known per se, for example by sintering without pressure of fine starting powder mixtures or by infiltration of porous shaped bodies of the sintered material components with the lowcarbon binder.

For carrying out these processes, very fine and very pure starting powders are advantageously used as a starting material. The borides and nitrides selected as the sintering material components should be as free as 'possible of carbon-containing impurities which have an adverse effect on the formation of the microstructure in the finished sintered body. Thus, for example, titanium diboride, which can contain boron carbide resulting from the preparation, can react during the sintering step in the presence of iron not only with graphite, as already mentioned above, but also with boron carbide to form the undesired FezB phase, as shown by the following equations: TiB, 4Fe C TiC 2FeB (1) TiBz 12Fe B 4 C TiC 6Fe 2 B (2) However, oxygen, which is usually present in the form of adhering oxides, for example TiO., does not interfere and can be tolerated up to about 2% by weight in the starting powders. Furthermore, it has been found that even a separate addition of oxides, in particular f I o II

I

o so 0 I to., 0 04040 0 0 00 0 0 04*4 .o~o 0 o 0 Ti0 2 does not interfere with the sintering step and that, for example, if up to 10% by volume of Ti0 2 are present in the finished mixed material, the properties of the latter remain virtually unchanged.

The low-carbon binder metals used are advantageously iron grades having a C content of less than 0.1 and preferably less than 0.05% by weight. Carbonyl iron powders having an Fe content from 99.95 to 99.98% by weight have proved particularly suitable. These lowcarbon iron grades can contain as alloy constituents, for example, chromium in cqugntities of about 12% by weight or nickel/chromium mixtures of, for example, 8% by weight of nickel and 18% by weight of chromium.

In order to avoid contamination esppe'?ially with carbon, it is advantageous autogenously to grind these starting powders, which must have an adequate purity even from the preparation. For this purpose, known grinding units can be used, such as ball mills, planetary ball mills and attritors, in which the grinding bodies and grinding vessels consist of a material identical to the process material, which is to be understood in the present case as, for example, titanium diboride and lowcarbon iron grades.

In grinding with grinding bodies of titanium diboride, in particular coarse startingj powders can be comminuted down to the desired grain fineness, while grinding bodies of low-carbon iron grades are suitable for adequate mixing of the starting powders, since the comminution effect of the sintering material components is here only small. In this case, the desired grain size distribution of the starting powders must thereafore already exist before grinding.

If necessary, temporary binders or pressing aids are added to the powder mixtures obtained after mixinggrinding, and the mixtures are rendered free-flowing by spray-drying.. They are then pr~ssed by conventional measures such as cold-isostatic pressing or by diepressing to form green compacts of the desired shape and having a density of at least 60% theoretical density.

-6- Binders and/or pressing aids are removed, without leaving a residue, by a heat treatment at 400 0 C. The green compacts are then heated, while excluding oxygen, to temperatures in the range from 1350°C to 1900°C, preferably from 1550°C to 1800°C, and held at this temperature for 10 to 150 minutes, preferably 15 to 45 minutes, until a liquid iron-rich phase has formed, and then slowly cooled to room temperature. This sintering step is advantageously carried out in furnace units which are fitted with metallic heating elements, for example of tungsten, tantalum or molybdenum, in order to avoid undesired carburization of the sintered bodies.

Subsequently, the sintered bodies can, preferably before cooling to room temperature, by applying pressure by means of a gaseous pressure transmission medium, such 0*o° as argon, be heated for a further 10 to 15 minutes at 0o 0 0 temperatures from 1200 0 C to 1400 0 C under a pressure from S• 0° 150 to 250 MPa, preferably about 200 MPa. As a result of this unconfined, hot-isostatic recompaction virtually all pores still present are eliminated so that the finished mixed sintered metal material has a density of 100% 9 theoretical density.

•o As an alternative to this sintering step, the sintering material components, for example titanium °0.'oo boride, titanium nitride and, if appropriate, titanium dioxide, can be ground per se autogenously and these powder mixtures can be pressed with shaping to give green compacts having a density of 50 to 60% theoretical density. These porous green compacts are then surrounded in a refractory crucible, for example of boron nitride or alumina, a powder fill which consists of the desired binder metal and which only partially covers the surface of the porous body. The crucibles are then heated in furnace units having metallic heating elements Ta, Mo) in a vacuum free of carbon impurities to temperatures above the melting point of the metallic binder phase, the molten binder metal penetrating by infiltration into the porous green compact, until the pores thereof are virtually completely closed. In this case too, virtually -7 pore-free mixed materials are obtained which likewise have a density of almost 100% theoretical density. The time required for this is determined essentially by the time needed to fuse the binder metal. Depending on the size of the workpiece, the process is in general complete within a period of from 30 seconds ro 30 minutes.

The mixed sintered metal materials according to the invention produced in this way are not only very dense, but also very hard, tough and strong. The desired combination of toughness and hardness can be varied within a wide range via the mixing ratio of the sintering materials since, for example, titanium nitride is somewhat tougher, at a slightly lower hardness, as compared with titanium diboride. Thus, for example, the crater oso wear normally occurring in throwaway cutting-tool tips can be already considerably reduced by small additions o of titanium nitride, even though such an influence was o0 not to be expected from a sintering material component which is softer relative to titanium diboride.

Owing to the combination of properties, which can in each case be precisely adapted to the desired applicatior, the mixed materials according to the invention are :equally suitable as cutting tools for machining very hard materials, for example SiC-reinforced aluminium alloys .S and nickel-based superalloys, as for impact-free working, such as core-drilling or sawing of silica-containing building materials, for example concrete.

The preparation of mixed sintered metal materials °~Oo according to the invention is described in more detail in the examples which follow.

Sintering materials and binder metals having the following powder analysers were used in Examples 1 to 7: _I 8 Table 1 Powder analyses of sintering material by weight) lement TiB 2 TiN Ti 67 >77 B 30.3 N 0.08 21.5 0 1 06 0.58 C 0.1 0.1 Fe 0.14 0.02 o 0 o .e0 a o o o Oa 0 a a 0 90 o 0 0 0 V 04 ~u Table 2 Powder analyses of binder metal by weight) xample No. 1 2 3 4 5 6 7 Fe >99.5 >99.5 >99.5 >99.5 >73.8 >99.5 >99.5 Ni 0 0 0 0 18 0 0 Cr 0 3 0 0 8 0 0 C <0.02 <0.02 <0.02 <0.02 <0.05' <0.05 i <0.05 Example 1 1350 g of titanium diboride having a mean particle size of 5 pm, 50 g of titanium nitride having a mean particle size of 2 pm and 600 g of carbonyl iron powder having a mean particle size of 20 pm were ground together with 2 g of paraffin and 10 dm 3 of heptane for 2 hours at 120 rpm in a grinding vessel of hot-pressed titanium diboride with grinding balls of titanium diboride. A free-flowing powder was prepared from the comminuted powder mixture having a mean particle size of 0.7 pm (FSSS), and this was pressed under a pressure of 320 MPa in a die press to give green compacts in the form of rectangular plates having dimensions of 53 x 23 mm.

The green compacts were then dense-sintered for ociaon. Registered Patent Attorneys To: THE COMMISSIONER OF PATENTS.

WATERMARK PATENT TRADEMARK ATTORNEYS 9 minutes at 1700"C in a furnace with tungsten heating elements in vacuo in the presence of a carbon-free residual gas and then slowly cooled to room temperature.

Example 2 1570 g of titanium diboride having a mean particle size of 5 pm, 110 g of titanium nitride of the same particle size and 300 g of carbonyl iron powder having a mean particle size of 20 pm were ground together with 1% by weight of paraffin and 10 dm 3 of heptane for 2 hours at 120 rpm in a grinding vessel of V2A stainless steel with carbonyl iron balls. The powder mixture thus obtained was processed and sintered as described in Example 0 1.

o 0 e0 Example 3 *Green compacts in the form of plates were prepared from the same quantities of titanium diboride, titanium nitride and carbonyl iron under the same conditions as described in Example 1, and these were sintered for 15 minutes at 1650 0 C in a carbon-free vacuum. After lowering the temperature to 1200 0 C, these pre-sintered o plates were hot-isostatically recompacted for 15 minutes in the same furnace chamber under an argon gas pressure of 200 MPa and then cooled slowly to room -emperature.

Example 4 1300 g of titanium diboride and 175 g of titanium nitride having a mean particle size of 10 pm were ground together with 10 dm 3 of heptane for 2 hours at 120 rpm in a grinding vessel of titanium diboride and grinding balls of titanium diboride. The comminuted sintering material powder mixture was then cold-isostatically pressed in a rubber envelope to give green compacts having a density of 60% theoretical density. These green compacts were placed into an alumina crucible and surrounded by a powder mixture of carbonyl iron which Sreached up to about 2 cm below the upper edge of the compacts. The crucibles were then heated to 1700 C in a 10 furnace with tungsten heating elements in a carbon-free vacuum and held for 30 minutes at this temperature.

During this time, the porous green compact absorbs molten iron until the pores are virtually completely closed.

Example The same quantities of titanium diboride and titanium nitride as in Example 1 were ground and further processed with 600 g of a powder of stainless steel containing 18% by weight of nickel, 8% by weight of chromium and <0.05% by weight of carbon and having a starting mean particle size of 20 pm under the same conditions as in Example 1. Sintering was carried out at a temperature of 1650°C.

oo9 S Example 6 1030 g of titanium diboride (60% by volume), o .9 :1 206 g of titanium nitride by volume), 164 g of titanium dioxide (10% by volume) and 600 g of carbonyl iron powder, the starting powders each having a mean particle size of 30 pm, were ground and further processed as described in Example 1.

99o9 a a o Example 7 9, 687 g of titanium diboride (40% by volume), 824 g of titanium nitride (40% by volume) and 600 g of carbonyl iron powder (20% by volume of Fe), the starting powders each having a mean particle size of 30 pm, were ground S for 2 hours at 120 rpm in a grinding vessel of V2A stainless steel and carbonyl iron balls. Further processing was carried out as described in Example 1.

The mixed sintered metal materials prepared in Examples 1 to 7 were analysed and tested for their mechanical properties. The results are compiled in Tables 3 and 4.

11 Table 3 Characterization of the sintered bodies ri

III,

El C

I

I,

o 0 000$ a~ 94 05 a C 0,-a

I

0404 0 4 00 0 a a 0 Cs is. ga 0 4 a a a a a Example No. 1 2 1 3 5 6 7 by volume of sintered material 80 90 80 50 80 80 by volume of TiB 2 78 85 78 45 78 60 by volume of TiN 2 5 2 5 2 10 by volume cf Ti 2 1 Grain size of the 2.5 5.5 3.0 2.5 2.3 2.1 Isintered material [pm] Grain size of the 1.6 3.5 1.9 1.0 1.5 1.5 1.8 binder phase [mm] IRelative density 99.1 98.9 99 .8 98 98.7 9C.5 99.2 [theoretical density] Table 4 Mechanical properties Example No. 1 2~ 3 4 5 6 7 30 hardness 1810 2080 1750 1220 1760, 1790 1620 Bending fracture 1250 1020 1350 1850 1400. 1200 1350 trength [MPa] racturee8s 9.21 8.1 9.3 16.3 10.2 9.0 10.3 t c Kc [MPa .Im] I

I

Claims (1)

12-- THE CLAIMS DEFINING THE INVENTION ARE AS FOLLOWS: 1. Mixed sintered metal materials based on high- melting borides and nitrides of the metals from Group 4b of the Periodic Table and low-melting metals consisting of iron and iron alloys, characterized in that the mixed materials consist of 40 to 97% by volume of borides selected from the group comprising titanium diboride, zirconium diboride and solid solutions thereof, 1 to 48% by volume of nitrides selected from the group comprising titanium nitride and zirconium nitride, S* 0 to 10% by volume of oxides selected from the group comprising titanium dioxide and zirconium dioxide and 2 to 59,% by volume of low-carbon iron and iron alloys and have the following properties: density at least 97% theoretical density, relative to the theoretically possible density of the total mixed material, grain size of the sintered material phase at most 5.5 pm, hardness (HV 30) at least 1,200, ,I bending fracture strength (measured by the 4-point method at room amperarure) at least 1,000 MPa and 5i°^nr=s M 1/2 fractureA iA te Kic at least 8.0 MPa m 2. Materials according to Claim 1, characterized in that the sintering material components I- n con- sist of titanium diboride and titanium nitride, which together make up 50 to 97% by volume of the total mixed material, and the sintering material component 3- consists of titanium dioxide in a proportion of 0.1 to by volume. 3. Mixed materials according to Claim 1 and 2, characterized in that the binder metal component JAJ i -consists of a low-carbon iron alloy which contains chromium or chromium/nickel mixtures as alloy S f constituents. 13 4. Process for producing the mixed materials according to Claim 1, characterized in that highly pure starting powders of the sintering material components, and if appropriate, the binder metal are autogenously ground and the fine starting powder mixtures thus obtained are cold-pressed with shaping to give green compacts having a density of at least 60% of theoretical and these are subsequently sintered without pressure in a carbon-free atmosphere and with exclusion of oxygen at temperatures in the range from 1350°C to 19000C and held at this temperature for 10 to 150 minutes. Process according to Claim 4, characterized in that the mixed materials sintered without pressure are, by applying pressure, hot-isostatica'!y recompacted by means of a gaseous pressure transmission medium at temperatures from 1200 0 C to 14000C under a pressure from 150 to 250 MPa for to 15 minutes. 6. Process for producing the mixed materials according to Claim 1, characterized in that highly pure starting powders of the sintering material components and, if appropriate, autogenously around, the fine starting powder mi pressee cPng toe gi< grpac .mixtures thus obtained are cold-pressed with shaping to give green compacts\ and these are heated under a powder fill of the binder metal component in a carbon-free atmosphere to a temperature above the melting point of the metallic binder phase until the molten binder metal penetrates by infiltration into the porous green compact and completely seals the pores thereof. D[ATED This 6th day of November, 1992 ELEKTROSCHMELZWERK KEMPTEM GmbH WATERMARK PATENT TRADEMARK ATTORNEYS THE ATRIUM 290 BURWOOD ROAD HAWTHORN VICTORIA 3122 AUSTRALIA